In fact, it explicitly DOES say that she effectively switched the sun off summarily, not gradually.
"Each night before midnight, Auril takes to the sky on the back of a white roc and weaves her spell, which manifests as a shimmering curtain of light—a beautiful aurora that illuminates the night sky and fades before dawn. This powerful magic prevents the next day’s sun from rising above the horizon, turning midday into twilight and trapping Icewind Dale in winter’s dark embrace, with no sunlight or warmth to melt the snow and ice."
"Ferocious blizzards make the mountain pass through the Spine of the World exceedingly treacherous, and this land has not felt the warmth of the sun in over two years."
You should probably read the book before you set about telling people how wrong their critiques are.
Seriously, why the compulsion to leap to the defense of something you haven't actually read? Aren't you concerned that you may not, you know, know what you're talking about?